Fundamental Food Microbiology, Third Edition - Fuad Fathir

CHARACTERISTICS OF PREDOMINANT MICROORGANISMS IN FOOD 29
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especially in meat products; stored at refrigerated temperature. Some strains produce
bacteriocins. Species: Carnobacterium piscicola.
Brochothrix. Similar in many characteristics to lactobacilli; facultative anaerobes;
homofermentative; nonmotile; found in meat. Can grow in refrigerated vacuumpackaged
meat and meat products. Species: Brochothrix thermosphacta.
Listeria. Short rods (0.5 ¥ 1 mm); occur singly or in short chains; motile; facultative
anaerobes; can grow at 1�C; cells killed by pasteurization. The species are widely
distributed in the environment and have been isolated from different types of foods.
Some Listeria monocytogenes strains are important foodborne pathogens.
8. Gram-Positive, Nonsporeforming Irregular Rods
Corynebacterium. Slightly curved rods; some cells stain unevenly; facultative anaerobes;
nonmotile; mesophiles; found in the environment, plants, and animals. Some
species cause food spoilage. Corynebacterium glutamicum is used to produce
glutamic acid.
Brevibacterium. Cells can change from rod to coccoid shape; aerobes; nonmotile;
mesophiles. Two species, Brevibacterium linens and Bre. casei, have been implicated
in the development of the aroma in several cheese varieties (surface ripened),
because of the production of sulfur compounds (such as methanethiol). In other
protein-rich products, they can cause spoilage (in fish). They are found in different
cheeses and raw milk.
Propionibacterium. Pleomorphic rods (0.5 ¥ 2 mm); can be coccoid, bifid, or branched;
present singly or in short chains; V and Y configuration and in clumps with Chinesecharacter-like
arrangement; nonmotile; anaerobes; mesophiles. Dairy propionibacteria
are used in food fermentation (Propionibacterium freudenreichii in Swiss
cheese). Produce proline and propionic acid. Found in raw milk, Swiss cheese, and
silage.
Bifidobacterium. Rods of various shapes; present singly or in chains; arranged in V
or star-like shape; nonmotile; mesophiles; anaerobes. Metabolize carbohydrates to
lactate and acetate. Found in colons of humans, animals, and birds. Some species
are used in probiotics (Bifidobacterium bifidum, Bif. infantis, Bif. adolescentis).
9. Some New Genera
Based on nucleic acid homology studies, several new genera have been created from
the existing genera. Some that are important in food microbiology are listed here.
Most of their characteristics are similar to those of the species in the respective old
genera. Examples include Tetragenococcus (from Pediococcus), Vagococcus (from
N-group Streptococcus), Weissella and Oenococcus (both from Leuconostoc), Kocuria
(from Micrococcus), Shewanella (from Pseudomonas), and Alicyclobacillus
(from Bacillus).
VI. IMPORTANT BACTERIAL GROUPS IN FOODS
Among the microorganisms found in foods, bacteria constitute major important
groups. 11 This is not only because many different species can be present in foods,